Bleeding time test is used to assess the function of platelets in human body. The aim of this project was thus to estimate the sample size required to determine the normal range of bleeding time (BT) in Borujerd (a city in Iran). A pilot study was designed to determine the range of normal BT in a small group of normal people. The total sample size for the next study was then calculated according to the results.
In order to determine the sample size, a total of 33 volunteers participated in this study. The normal range of BT was determined by Ivy method. Written informed consents were obtained from all participants and their clinical history was recorded. The sampling was performed once for each participant. However, the results were interpreted by two observers. The study protocol was approved by the Ethics Committee of the research center at Lorestan University of Medical Sciences (Iran).
In this study, 33 normal participants (20 women and 13 men) were divided into four age groups of 35-44, 45-54, 55-64 and over 64 years old. Maximum and minimum BTs in men were 209 (in the age group of 35-44 years) and 150 seconds (in the age group of over 64 years), respectively. On the other hand, the corresponding values in women were 194 (in 55-64 year-old subjects) and 145 seconds (in women over 64 years of age). Considering the aforementioned results, the total sample size for the next study was determined to be 580 normal subjects by two-sample t-test power analysis at a power of 0.91816.
There was a significant difference between the normal range of BT in participants of Borujerd and previously recorded range in other studies. Moreover, normal BT in men decreased by aging. This study did not show any special order in increasing or decreasing BT in women.